1. Role and Deficiency Symptoms of Secondary Nutrients in Rice

2. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Introduction
In today’s agriculture with the emphasis on higher crop yields, there is an increased need for calcium, magnesium and sulphur, called secondary nutrients.
Some of the factors responsible for this increased need are:
Increased use of higher analysis fertilizers.
Increased crop yields.
High crop utilization of calcium, sulphur and magnesium.

3. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Introduction
Decreased use of sulphur containing insecticides and fungicides
Government restrictions on sulphur emissions to the atmosphere.
Many soils are acidic and need limestone, which provides calcium.
Many soils are deficient in sulphur and magnesium.
Increased awareness of sulphur and magnesium needs.

4. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Sulphur (S): role in rice
It is a constituent of essential amino acids (cysteine, methionine, and cystine) involved in chlorophyll production and is thus required for protein synthesis, and plant function and structure.
Sulphur is also a constituent of coenzymes required in protein synthesis. It is contained in the plant hormones thiamine and biotine, both of which are involved in carbohydrate metabolism.
S is also involved in some oxidation-reduction reactions.
It is less mobile in the plant than N so that deficiency tends to appear first on young leaves. S deficiency affects human nutrition by causing a reduction in cysteine and methionine content in rice.

5. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Sulphur deficiency in rice:

6. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Causes of S deficiency
Low status of S in the soil.
Depletion of soil S as a result of intensive cropping systems.
Use of S-free fertilizers
S concentrations in groundwater, however, may range widely. Irrigation water contains only small quantities of SO42-.
S contained in organic residues is lost due to burning.

7. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Occurrence of S deficiency in soils
Soils containing allophane (e.g., Andisols)
Soils with low organic matter status.
Highly weathered soils containing
large amounts of Fe oxides.
Sandy soils, which are easily leached.

8. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Corrective measures of S deficiency
S deficiency is easily corrected or prevented by using S-containing fertilizers (Table 1)
Table 1. Sulphur containing fertilizers for rice
Name
Formula
Content
Comments
Ammonium sulphate
(NH4)2SO4
24% S
Quick-acting
Single superphosphate
Ca(H2PO4)2 . H2O + CaSO4 . 2 H2O
12% S, 7–9 % P, 13–20% Ca
Soluble, quick-acting
Potassium sulphate
K2SO4
18% S
Magnesium sulphate (Epsom salt)
MgSO4 . 7 H20
13% S, 10% Mg
Very quick-acting
Kieserite
MgSO4 . H20
23% S, 17% Mg
Langbeinite
K2SO4 . MgSO4
18% K, 11% Mg, 22% S
Gypsum
CaSO4 × 2 H2O
17% S
Slow-acting
Elemental S S
97% S
S-coated urea
CO(NH2)2 + S
6–30% S, 30–40% N

9. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Magnesium (Mg): role in rice
Magnesium activates several enzymes.
It is a constituent of chlorophyll, and is involved in CO2 assimilation and protein synthesis.
Mg also regulates cellular pH and the cation-anion balance.

10. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Magnesium deficiency symptoms in rice
It is very mobile and is retranslocated easily from old leaves to young leaves. Deficiency symptoms therefore tend to occur initially in older leaves.
Mg-deficient plants are pale-coloured with interveinal chlorosis first appearing on older leaves, and later on younger leaves as deficiency becomes more severe.
Green coloring appears as a "string of beads" compared with K deficiency, in which green and yellow stripes run parallel to the leaf.

11. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Magnesium deficiency symptoms in rice
Leaf number and leaf length are greater in Mg-deficient plants and Mg-deficient leaves are wavy and droopy due to an expansion in the angle between the leaf sheath and leaf blade.
With moderate deficiency, plant height and tiller number are not affected greatly.
Reduced number of spikelets and reduced 1,000-grain weight. May reduce grain quality (% milled rice, protein, and starch content).

12. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Magnesium deficiency symptoms in rice
Orange-yellow interveinal chlorosis
usually appears first on older leaves
Chlorosis may also appear on the flag leaf.

13. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Magnesium deficiency symptoms in rice
Mg deficiency may also be induced by large applications of K fertilizer on low Mg status soils (IRRI, Phillipines)

14. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Causes and occurrence of Mg deficiency
Important cause of Mg deficiency is low available soil Mg. Furthermore, decreased Mg uptake due to a wide ratio of exchangeable K:Mg (i.e., >1:1) causes its deficiency.
Mg deficiency is more common in rainfed lowland and upland rice where soil Mg has been depleted because of the continuous removal of Mg in crop products without recycling crop residues or replacing removed Mg with mineral fertilizer. Many rainfed rice soils are inherently deficient in Mg.

15. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Corrective measures of Mg deficiency
Apply Mg-containing fertilizers (Table 2). Rapid correction of Mg deficiency symptoms is achieved by foliar application of liquid fertilizers containing Mg (e.g., MgCl2).
Table 2. Magnesium containing fertilizers for rice.
Name
Formula
Content
Comments
Kieserite
MgSO4 . H20
17% Mg, 23% S
Soluble, quick-acting
Langbeinite
K2SO4, MgSO4
18% K, 11% Mg, 22%S
Quick-acting
Magnesium chloride
MgCl2
9% Mg
Magnesium oxide
MgO
42% Mg
Slow-acting, for foliar application
Magnesite
MgCO3
25-28% Mg
Slow-acting
Dolomite
MgCO3. CaCO3
13% Mg, 21% Ca
Slow-acting, content of Ca and Mg varying

16. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Calcium (Ca): role in rice
Calcium is a constituent of Ca pectates, important cell wall constituents also involved in biomembrane maintenance.
Helps in cell wall stabilization as an enzyme activator, in osmoregulation, and in the cation-anion balance.
Ca is less mobile in rice plants than Mg and K. Because Ca is not retranslocated to new growth, deficiency symptoms usually appear first on young leaves. Ca deficiency also results in impaired root function and may predispose the rice plant to Fe toxicity.
An adequate supply of Ca increases resistance to diseases such as bacterial leaf blight or brown spot.

17. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Calcium deficiency symptoms in rice
Symptoms are usually visible only under severe Ca deficiency (e.g., pot experiments, exhaustion experiments).
The tips of the youngest leaves become white or bleached, rolled, and curled.
Necrotic tissue may develop along the lateral margins of leaves and old leaves eventually turn brown and die.
Ca deficiency may resemble B deficiency and plant tissue analysis may be required to distinguish the cause of symptoms.

18. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Calcium deficiency symptoms in rice
The tips of the youngest leaves may become chlorotic-white (IRRI, Phillipines)

19. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Causes of Ca deficiency
Small amounts of available Ca in soil (degraded, acid, sandy soils)
Alkaline pH with a wide exchangeable Na:Ca ratio resulting in reduced Ca uptake. Use of irrigation water rich in NaHCO3.
Excessive N or K fertilizer application resulting in wide NH4:Ca or K:Ca ratios and reduced Ca uptake.
Excessive P fertilizer application, which may depress the availability of Ca (due to formation of Ca phosphates in alkaline soils).

20. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Occurrence of Ca deficiency in soils
Acid, strongly leached, low-CEC soils in uplands and lowlands
Soils derived from serpentine rocks
Coarse-textured sandy soils with high percolation rates and leaching
Leached, old acid sulphate soils with low base content

21. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Corrective measures of Ca deficiency
Apply CaCl2 (solid or in solution) or Ca-containing foliar sprays for quick treatment of severe Ca deficiency.
Apply gypsum on Ca-deficient nonacidic soils, e.g., on sodic and high-K soils.
Apply lime on acid soils to raise pH and Ca availability.
Apply Mg or K in conjunction with Ca because Ca may cause deficiencies in these nutrients.
Apply pyrites to mitigate the effects of NaHCO3-rich water on Ca uptake.

22. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Corrective measures of Ca deficiency
Table 3. Calcium containing fertilizer sources for rice.
Name
Formula
Content
Comments
Calcium chloride
CaCl H2O
18% Ca
Soluble, quick-acting, does not raise pH
Gypsum
CaSO H2O
23% Ca, 18% S
Slightly soluble, slow-acting, for saline and alkaline soils
Dolomite
MgCO3 + CaCO3
13% Mg, 21% Ca
Slow acting , content of Ca and Mg varying
Lime
CaCO3
40% Ca
Slow-acting, for acid soils

23. Role and Deficiency Symptoms of Secondary Nutrients in Rice
Let us sum up
Calcium, magnesium and sulphur are essential for rice crop.
Variety of roles are being played by these
secondary nutrients in rice
Their deficiency under certain situations produces varying symptoms, which eventually affect the growth and yielding ability of rice.
The deficiency of sulphur is more common than deficiency of calcium and magnesium in rice soils in India.
The deficiency of these nutrients can be corrected by applying appropriate fertilizers and crop management practices.